AU1654792A

AU1654792A - Arc quenching apparatus for circuit breakers

Info

Publication number: AU1654792A
Application number: AU16547/92A
Authority: AU
Inventors: Kari Luoma
Original assignee: ABB Stromberg Sahkonjakelu Oy
Current assignee: ABB Stromberg Sahkonjakelu Oy
Priority date: 1991-05-06
Filing date: 1992-05-04
Publication date: 1992-12-21
Anticipated expiration: 2012-05-04
Also published as: FI87614B; FI87614C; SE513663C2; FR2676317A1; NO934020L; SE9303506D0; IT1263203B; US5403983A; DE4291335T1; ITTO920382A1; GB2274205B; ITTO920382A0; NO934020D0; GB2274205A; AU655263B2; FR2676317B1; DE4291335C2; GB9321375D0; NO305926B1; WO1992020083A1

Description

Arc quenching apparatus for circuit breakers

The invention relates to an arc quenching apparatus for circuit breakers, based on a plate chamber construction. The apparatus comprises a quenching space in which each phase has a stationary contact and a knife contact pivotable in relation thereto, and which has a quenching chamber in whose body member, made of an insulating material, quench- ing plates are disposed in a spaced-apart relation so as to be located successively in relation to the path of the opening movement of the knife contact. The arc quenching installation according to the invention is particularly suitable for use in SF₆-insulated medium- voltage circuit breakers.

A basic construction of the kind described above is known for instance from the Applicant's ear¬ lier load circuit breaker of the type OETL 250...3150 (the figures refer to ampere values) , wherein the quenching plates are disposed in the form of a cir¬ cular arc substantially perpendicularly to the tan¬ gent of the path of the knife contact.

Another extinguishing apparatus based on a plate chamber construction is known from European Patent 0 157 242. In this apparatus, a stationary contact and a quenching chamber are disposed on a busbar. The quenching plates of the quenching chamber are disposed in the chamber in parallel with the tan¬ gent of the starting point of the path of the knife contact and in a spaced-apart relation, and further superposed with an overlap so that the distance bet¬ ween the movable knife contact and the quenching plates increases as the opening movement of the knife contact proceeds. The advantage with the quenching installations of the type described above, based on a plate chamber construction, is that the actual circuit breaking operation is successful with a small amount of energy. However, the problem with this apparatus has been found to be that the arc will produce a layer of soot on the quenching plate support structure made of an insulating material, and this soot layer will make the support structure conductive between the quench¬ ing plates. As a result, the breaking capacity of the circuit breaking apparatus is strongly impaired.

The purpose of the present invention is to remove this problem and to achieve an arc quenching apparatus by means of which the breaking capacity of a circuit breaker based on the plate chamber prin- ciple can be made considerably better than hereto¬ fore. This is achieved with the apparatus of the invention, which is characterized in that stop means are disposed between the ends of the quenching plates on the knife contact side and the body member, said stop means preventing direct contact with the body member at least in the spaces between the quenching plates.

The basic idea of the invention is to introduce between the ends of the quenching plates on the knife contact side and the support structure of the quench¬ ing plates (the body member of the quenching cham¬ ber), which is made of an insulating material, means preventing direct contact with the body member at least between the quenching plates, thus preventing the passage of the arc to the support structure or to the vicinity thereof. Said means can also be located over the topmost quenching plate and under the lower¬ most quenching plate.

The improved breaking capacity achieved on account of the invention means that the breaking will be successful with currents markedly higher than heretofore, or, correspondingly, that with the same current values a considerably higher number of break¬ ing times than heretofore is achieved. In accordance with two advantageous embodiments of the invention, the stop means are constituted by ridges or steps made in the quenching plates. Thus one avoids using separate barrier members, and the stop means are easy to manufacture for instance in connection with the die cutting of the quenching plates.

The invention will be explained in more detail in the following, with reference to examples accord¬ ing to the accompanying drawings, wherein Figure la is a side view of an apparatus according to a first embodiment of the invention,

Figure lb is a view of an apparatus according to Figure la taken along line I-I of Figure la and without the topmost quenching plates, Figure 2a is a side view of an apparatus according to another embodiment of the invention,

Figure 2b is a view of an apparatus according to Figure 2a taken along line II-II of Figure 2a and without the topmost quenching plates, Figure 3a is a side view of an apparatus according to a third embodiment of the invention,

Figure 3b is a view of an apparatus according to Figure 3a taken along line III-III of Figure 3a and without the topmost quenching plates, and Figure 4 is a top view of an quenching plate according to an alternative embodiment.

Figures la and lb show a quenching apparatus according to a first embodiment of the invention. In this apparatus, a circuit breaker is disposed in a quenching space 10 within a gas-tight box (not shown), the circuit breaker comprising a stationary contact 11 connected to a first element 1 of the cur¬ rent path, and a movable knife contact 12 connected to a second element 2 of the current path by pivoting it thereto by means of a fulcrum pin 3. The knife contact is guided by guide means known per se (not shown) between a closed position and an open posi¬ tion. In Figure la, the knife contact has been shown in the closed position wherein its tip 12c touches the stationary contact 11. The knife contact com¬ prises two parallel knives 12a and 12b (Figure lb) that are pressed against one another by means of springs 17 to produce an appropriate contact force on the contact surfaces. To improve the breaking capa- city, the quenching space 10 is filled with an extin¬ guishing and insulating medium in a manner known per se, said medium advantageously being sulphur hexa- fluoride (SF₆) or some mixture thereof.

A quenching chamber 13 is attached to the sta- tionary contact 11, said chamber being composed of a body member 15 made of an insulating material, such as plastic, and quenching plates 14 supported there¬ to and being substantially parallel and spaced apart. In this exemplary case, there are six quenching plates of a material suitable for this purpose, such as coated (zinc coated) steel plates. The body member 15 of the quenching chamber comprises in accordance with the invention a lower portion 15a fixed to the stationary contact and a fixing shaft 15b extending obliquely upwards therefrom, to which shaft the quenching plates 14 are attached so that each quench¬ ing plate extends from its end facing the body mem¬ ber to both sides of the fixing shaft 15b.

As the circuit breaker opens, the tip of the knife contact travels a path having the form of a circular arc, which has been indicated with a broken line P. Grooves 16 (Figure lb) are formed in the ends of the quenching plates 14 on the knife contact side, and edge flanges 16' are formed in each quenching plate. The tip of the knife contact extends to the space constituted by the groove and travels in this space during its movement. The distance of the tip of the knife contact from the front edge 16a of the groove is approximately equal to its distance from the lateral edges 16b of the groove, and the succes¬ sive plates 14 are disposed in relation to the path of the opening movement so that the distance of the tip of the knife contact from the quenching plates remains the same when the opening movement proceeds. By means of the grooves in the front edges of the quenching plates, the control of the arc can be im¬ proved. The use of said grooves for this purpose is known per se.

As the knife contact is detached from the sta- tionary contact, an arc is immediately generated therebetween. As the opening movement proceeds, the arc is divided so that base points are generated therefor also in the quenching plates. In order to ensure that the arc will remain burning between the quenching plates 14 and cannot soot the body member 15, transverse ridges 20 are formed in the quenching plates, said ridges preventing direct contact with the body member 15 in the spaces 22 between the quenching plates. In order to prevent direct (op- tical) contact, the ridges have at least partly been arranged with an overlap, and the height of each ridge is at least equal to the distance between the plates. Besides that the ridges prevent the passage of the arc to the vicinity of the body member 15, they also prevent the propagation of heat radiation to the body member.

An apparatus according to another embodiment of the invention has been shown in Figures 2a and 2b. In this case, the construction is otherwise the same but the ridges in the quenching plates have been replaced with transverse barrier plates 21a and 21b, which are disposed on the lower and upper surface of each quenching plate respectively. The barrier plates 21a and 21b on the upper and lower surfaces are displaced in the longitudinal direction of the quenching plate to different positions, and thus the barrier plates on the upper surface of the lower quenching plate and on the lower surface of the upper quenching plate together prevent direct contact with the body member 15 in each intermediate space 22. The height of the barrier plates in the same intermediate space is thus smaller than the distance between the quenching plates, but their total height is at least equal to the distance between the plates. Figures 3a and 3b show an apparatus according to a third embodiment of the invention. The construc¬ tion is still the same, except that the ridges or barrier plates have in this case been replaced with steps 31 provided in the quenching plates, said steps being displaced in the longitudinal direction of the quenching plates to have an overlap. In order to pre¬ vent direct contact with the body member 15 in the intermediate space 22, the height of each step in this case is at least equal to the distance between the quenching plates.

The ridges, barrier plates, steps or the like disclosed above need not necessarily extend directly in the transverse direction of the quenching plates as set forth hereinabove, but they can be shaped for instance in the manner shown in Figure 4 so as to extend from the leading edge of one edge flange 16' around the groove 16 in the quenching plate to the leading edge of the opposing edge flange 16', and thus they also prevent the blowing of the arc to the sides of the quenching chamber, which might cause a disruptive discharge between the phases or to the earth. Also, since the stop means in this case give better protection in the lateral direction, the body member of the quenching chamber need not be located centrally. Thus in the example of Figure 4, the body member is constituted in a known manner by separate side walls 41 between which the quenching plates are fixed. The stop means, which in this example have been shown as a ridge having the cross-section of a circular arc, are denoted by reference numeral 42. However, if additional protection is not needed on the sides of the quenching chamber, the attachment of the quenching plates in accordance with the examples of Figures la - 3b to a body member constituted by a single piece only is advantageous in that it makes possible simpler (straight) stop means.

Even though the invention has been explained in the foregoing with reference to an example according to the accompanying drawing, it is obvious that the invention is not restricted thereto, but it can be modified in many ways within the scope of the inven¬ tive concept disclosed in the attached claims. For instance, the quenching plates need not be parallel, and all of them need not be disposed at the same dis- tance from the tip of the knife contact. The shape and number of the ridges can vary in accordance with how the quenching plates are disposed in relation to one another: the ridges may, for instance, have the shape of a circular arc and be vertically aligned. The ridges can also replace the barrier plates in such a way that there is a ridge corresponding to a barrier plate on the upper and lower surface of each plate. The barrier plates can in principle also be replaced with a barrier net, but this is not as secure an arrangement as a barrier plate. However, the blocking of a direct contact with the body member is to be understood to encompass also arrangements based on barrier nets. Even though the arc quenching installation according to the invention is suitable for use particularly in connection with medium-vol¬ tage circuit breakers (in the voltage range 1 kV - about 36 kV), the same principle can also be applied in the low and high voltage ranges.

Claims

Claims :

1. An arc quenching apparatus for circuit breakers, comprising a quenching space (10) in which each phase has a stationary contact (11) and a knife contact (12) pivotable in relation thereto, and which has a quenching chamber (13) in whose body member (15), made of an insulating material, quenching plates (14) are disposed in a spaced-apart relation so as to be located successively in relation to the path (P) of the opening movement of the knife contact (12), c h a r a c t e r i z e d in that stop means (20, 21a, 21b, 31, 42) are disposed between the ends of the quenching plates (14) on the knife contact (12) side and the body member (15), said stop means preventing direct contact with the body member (15) at least in the spaces (22) between the quenching plates (14) .

2. An apparatus as claimed in claim 1, c h a r a c t e r i z e d in that the stop means are constituted by ridges (20) formed in the quenching plates (14) .

3. An apparatus as claimed in claim 1, c h a r a c t e r i z e d in that the stop means are constituted by steps (31) formed in the quenching plates (14).

4. An apparatus as claimed in claim 1, c h a r a c t e r i z e d in that the stop means are constituted by barrier plates (21a, 21b) fitted to the quenching plates (14) .

5. An apparatus as claimed in any one of claims 1 to 4, c h a r a c t e r i z e d in that the quenching plates (14) are attached to a fixing shaft (15b) of the body member so that each quenching plate extends from its end facing the body member to both sides of the fixing shaft (15b).

6. An apparatus as claimed in any one of claims 1 to 5, wherein the tip (12c) of the knife contact (12) travels in a groove (16) formed in the quench¬ ing plates (14), c h a r a c t e r i z e d in that the stop means (42) extend about the groove.